The present invention relates to systems (sensors) designed to measure full angular orientation and position of an object relative to another object. In munitions and other similar applications, such a system provides an absolute onboard referencing system, in which the munitions is provided by its full position and orientation information relative to one or more ground stations or other mobile platforms during the flight. In munitions applications, this full position and orientation referencing system offers advantages over other position and orientation measurement systems (sensors) for guidance and control of smart munitions. In munitions applications, other advantages of the present position and orientation measurement system include: (1) the capability of a smart munitions with such a sensing system to be capable of determining its position and orientation while in flight with respect to one or more ground stations or other moving platforms, (2) the capability of a munitions to have autonomous position and orientation system, and (3) the position and orientation sensing system will be minimally intrusive and consume relatively low power.
For a moving object such as a smart munition to be guided or its motion altered or controlled, the control system that provided guidance and control action must have real-time information about the position and orientation of the object. In general and depending on each specific application, the position and orientation may be those of the moving object relative to a ground station, or relative to another moving platform.
To meet the requirements of the U.S. Army's future needs in the areas of precision-guided direct- and indirect-fire munitions, it is important that the position and orientation sensors be capable of being integrated reliably and economically into small- and medium-caliber munitions as well as long-range munitions. In particular, it is desirable to embed such sensors in the munitions, and that the sensors be autonomous and provide onboard position and orientation information relative to a ground station or other moving platforms.
Currently, radar-based guidance, often augmented by Global Positioning System (GPS) data, is used to determine information related to the position of munitions. Radar-based guidance of munitions is based upon the use of radio frequency (RF) antennas printed or placed on the surface of munitions to reflect RF energy emanating from a ground-based radar system. The reflected energy is then used to track the munition or the stream of bullets on the way to the target. The surface printed or placed antennas are, however, not suitable for munitions applications since they cannot survive the firing environment and readily loose their accuracy. Such surface printed or placed antenna based sensors also require large amount of power for their operation, and are very sensitive to geometrical variations and tolerances.
Corrections to a munition's flight path are currently possible but only if the munitions are equipped with an additional suite of internal sensors such as Inertia Measurement Unit (IMU's), accelerometers, and gyroscopes. Global Positioning Signals (GPS) are also used alone or in combination with other sensors such as accelerometers and gyroscopes. However, the inertia based sensors are relatively complex and inaccurate, occupy a considerable amount of volume, consume a large amount of power, are prone to drift and settling problems, and are relatively costly. The GPS sensors cannot provide orientation information and are prone to the loss of signal along the path of travel.
Furthermore, the current IMU technology cannot be implemented for munitions that are subjected to extremely high acceleration rates during firing, such as medium and small caliber munitions. High performance munitions may be subjected to accelerations in excess of 100,000 Gs. In general, inertia based sensors have not been successfully developed to survive firing accelerations of 30,000 Gs and over and also be capable to have measurement sensitivity to measure low acceleration levels required for guidance and control purposes.
It is readily appreciated by those familiar with the present art that the issues and concerns that were described above for munitions are generally true for all mobile platforms.
A need therefore exists for position and orientation measurement systems (sensors) in general, and for those that could be mounted or embedded into various moving platforms for their guidance and control. In munitions applications in particular, the full position and orientation (pitch, yaw and roll) information will define the motion of munitions in-flight and allows it to be guided towards its target.